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Improve Unreliable Bed Leveling (and ditch end of purge blob)
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@karrad, as you know I've been vocal about highly disliking the bed leveling inconsistency, so I've been trying some things to improve it and would like to provide this for consideration.

I know in task T1506 you are looking at how we can avoid bed leveling every time and I'm still stoked about that idea, but in the meantime I want to offer this as it will help in general (I beleive)

I've been working on this on and off for a couple weeks and have been running new startup gcode now for about a week solid with no problems. Has it improved things? Yes, I think so, at least to some degree.

Here is my logic ...

We know even the slightest amount of plastic (ooze or leftover) on E1 will create a bad bed level.

It struck me that you wipe E1 first then E2 - well during that time E1 has time to ooze - yes, I know the temps are lower during the wipe, but there is still ample time for stuff to sneak out.

So here is what I did:

  • Change to wipe E2 first, then wipe E1 to lessen chance for E1 to have time to ooze during E2's wipe when that was originally done second.
  • Turn fan on full speed during entire wipe sequence - this seems to more consistently blow stuck crap off.
  • During the original wipe sequence, at the end of it for each extruder, raise Z higher than it had been before.
  • After the original wipe sequence of E1 (which now happens second), introduced an additional short wipe sequence.
  • This new wipe sequence goes 0.25mm further into the pad and wipes at a (sort of) diagonal from one end of the pad to the other; the first part goes slow then the second part goes fast and Z raises high and waits 3 seconds between the slow/fast parts. The idea here is two-fold; first, because it is moving somewhat laterally the entire distdance, it seems to push crap off the nozzle tip better and secondly, I think it also has the effect of "pushing" the pad material back towards the center of the pad, thus reducing the left over center groove that appears after numerous wipes. If it is reducing the grooving that will improve the first wipe sequences chance of success as more material will press against the nozzle.
  • The last thing I did was get rid of that annoying and interferring (for large prints) blob that E1 leaves after the purge; I thought I had created a task for that, but maybe we had just talked about that via e-mail.
  • I've run the above for a while, but then additionally, found that raising the soften AND wipe temperatures by ~30C makes a big difference - the original wipe sequence does it's thing at this higher temp (if you of course adjust the profile to make the temps higher) then BEFORE starting the new wipe sequence I introduced, it issues the command to lower to the probe temp, BUT not wait for it to lower - I have found that by the time this second wipe sequence is done, the probe temp has lowered to it's target perfectly.
  • One other thing I did is E1/E2 shear off height were not matched - so I matched those and went from 0.45 to 0.35 so be aware of that.

When I've been testing this I have absolutely not touched the hot end at all after previous prints - I even have left 10mm+ strings hanging from the tip just to see what happens. Early on when I was testing this I got 9 perfect levels out of 11. In my most recent testing I'm up to 5 perfect levels in a row.

I would love for you guys to consider this new start up gcode - even if it doesn't perfectly fix everything, I do believe the logic is sound on the what and why of this new startup code. And even if you don't like this for some reason, the stupid blob is fixed :-).

Okay, tell me what is wrong with what I did :-) ... !!!

I have attached the new startup gcode:

Event Timeline

bmh created this task.Sat, Aug 31, 6:50 AM